Outboard motor

ABSTRACT

In an outboard motor, a feed passage, through which a lubricating oil that flows upward from a gear mechanism due to rotation of the gear mechanism, extends upward from a gear chamber and includes a first feed passage that extends from the gear chamber to a connection passage via a first upstream passage, a spiral passage, and an interior of an upper bearing, in that order. The feed passage further includes a second feed passage that extends from the gear chamber to the return passage while bypassing the spiral passage via a bypass passage. The bypass passage includes two ends spaced apart in a circumferential direction of the driveshaft and is disposed around the spiral passage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2017-084669 filed on Apr. 21, 2017. The entire contentsof this application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an outboard motor.

2. Description of the Related Art

U.S. 2013/0052891 A1 discloses an outboard motor including a gear casedisposed underwater and a gear mechanism housed inside the gear case andlubricated by a lubricating oil. The lubricating oil is stored in a gearchamber provided in the gear case. The lubricating oil inside the gearchamber is thrown upward due to rotation of a bevel gear included in thegear mechanism and fed upward to an oil slinger provided at adriveshaft. The lubricating oil supplied to the oil slinger is guidedupward along a spiral oil groove due to rotation of the driveshaft. Thelubricating oil is thus supplied to an internal gap of a tapered rollerbearing that rotatably supports the driveshaft. The lubricating oil thathas passed upward through the tapered roller bearing is returned to thegear chamber by a main lubrication circulation portion and a sublubrication circulation portion.

JP S57-182595 A discloses an example of a conventional circulation pathfor a lubricating oil. As in U.S. 2013/0052891 A1, the lubricating oilinside a gear chamber of JP S57-182595 A is fed upward due to rotationsof a pinion, a forward drive gear, and a reverse drive gear. Thelubricating oil is fed from the gear chamber to an insertion space via alower communication passage extending upward from the gear chamber. Asleeve surrounding a driveshaft is disposed at the insertion space. Thelubricating oil supplied to the insertion space enters inside the sleevefrom an opening portion that opens at an outer peripheral surface of thesleeve and is fed upward by a spiral lead portion provided on an innerperipheral surface of the sleeve. The lubricating oil is supplied to anupper bearing via an oil feed portion extending upward from the leadportion. The lubricating oil supplied to the upper bearing flowsdownward between an inner peripheral surface of the insertion space andthe outer peripheral surface of the sleeve and is discharged from theinsertion space via an upper communication passage positioned at aheight between the upper bearing and the lead portion. An outer diameterof a passage defined between the inner peripheral surface of theinsertion space and the outer peripheral surface of the sleeve isgreater than an outer diameter of the driveshaft.

With a conventional outboard motor, a lubricating oil is circulated in acirculation path provided in an interior of a lower case that isdisposed underwater. Gears, bearings, etc., are thus lubricated andthese members are cooled by the lubricating oil. The lubricating oilthat has cooled the gears, etc., is cooled by the lower case, etc.,while circulating through the circulation path. A temperature of thelubricating oil is thus maintained within an appropriate range. However,since the amount of heat generated in the lower case increases as gearsand other rotating bodies are made larger and outboard motors are madeto have a higher output, a temperature increase of the lubricating oilmust be minimized to prevent the temperature of the lubricating oil fromexceeding the appropriate range.

A temperature increase of the lubricating oil is suppressed byincreasing a total amount of the lubricating oil circulating inside thelower case because a heat capacity of the lubricating oil as a whole isthus increased. Also, a temperature increase of the lubricating oil isdecreased without increasing the total amount of the lubricating oil byimproving the circulation efficiency of the lubricating oil, that is, bypreventing stagnation of the lubricating oil or increasing a circulationflow rate of the lubricating oil because heat radiation from thelubricating oil will then be performed effectively.

However, with the method of increasing the total amount of thelubricating oil, an oil storage chamber storing the lubricating oilinside the lower case must be enlarged. Depending on the outboard motor,it may not be possible to provide a lower case with such a large oilstorage chamber. Also, when the lower case is enlarged to enlarge theoil storage chamber, the outboard motor has a lower propulsionefficiency because of the increased resistance of water applied to theoutboard motor.

With the outboard motor of U.S. 2013/0052891 A1, two lubricationcirculation portions (the main lubrication circulation portion and thesub lubrication circulation portion) that return the lubricating oilthat has lubricated the tapered roller bearing to the gear chamber areprovided to smoothly circulate the lubricating oil without enlarging thegear case. However, the circulation flow rate of the lubricating oil isdependent on a supply capacity of the oil slinger that feeds thelubricating oil to the tapered roller bearing and, therefore, thelubricating oil cannot be circulated at a flow rate exceeding the supplycapacity of the oil slinger. That is, unless the lubricating oil supplycapacity at the oil slinger is increased, the circulation flow rate ofthe circulation system as a whole cannot be increased even if the sublubrication circulation portion is added.

A flow rate of the lubricating oil supplied to the oil slinger due torotation of the bevel gear and a flow rate of the lubricating oil fed bythe oil slinger both increase with an increase of engine speed. However,during high speed rotation, the flow rate of the lubricating oilsupplied to the oil slinger due to rotation of the bevel gear becomesgreater than the flow rate of the lubricating oil fed by the oilslinger. Even when the flow rate of the lubricating oil supplied to theoil slinger exceeds the flow rate of the lubricating oil fed by the oilslinger, the lubricating oil will not be circulated at a flow rateexceeding the supply capacity of the oil slinger. Further, in this case,the lubricating oil stagnates between the bevel gear and the oilslinger, so that a pressure of the lubricating oil increases and thetemperature of the lubricating oil increases.

Similarly with the outboard motor of JP S57-182595 A, the lubricatingoil cannot be circulated at a flow rate exceeding a supply capacity ofthe spiral lead portion.

SUMMARY OF THE INVENTION

In order to overcome the previously unrecognized and unsolved challengesdescribed above, preferred embodiments of the present invention provideoutboard motors including a prime mover, a driveshaft extending in anup/down direction below the prime mover and to which a rotation of theprime mover is transmitted, a gear mechanism coupled to a lower end ofthe driveshaft and to which a rotation of the driveshaft is transmitted,a propeller shaft to which a rotation of the gear mechanism istransmitted, a lower case defining a gear chamber housing the gearmechanism and a lubricating oil and in which the driveshaft is inserted,an upper bearing located above the gear mechanism and rotatablysupporting the driveshaft inside the lower case, a feed passage throughwhich the lubricating oil flows upward from the gear mechanism due torotation of the gear mechanism extending upward from the gear chamber, areturn passage separate from the feed passage and that returns thelubricating oil, fed by the feed passage, to the gear chamber, and aconnection passage that guides the lubricating oil from the feed passageto the return passage.

The feed passage includes a first feed passage, including a firstupstream passage, extending upward from the gear chamber, and a spiralpassage that spirally surrounds the driveshaft below the upper bearingand extends from the gear chamber to the connection passage via thefirst upstream passage, the spiral passage, and an interior of the upperbearing, in that order, and a second feed passage including a bypasspassage that is disposed around the spiral passage, separate from thespiral passage, and includes two sides spaced apart in a circumferentialdirection of the driveshaft, and extending from the gear chamber to thereturn passage while bypassing the spiral passage with the bypasspassage.

With the above structure, when the prime mover rotates the driveshaft,the gear mechanism housed in the gear chamber of the lower case rotatesand the lubricating oil inside the gear chamber is fed upward. Thelubricating oil is thus made to flow through the first upstream passage,the spiral passage, and the interior of the upper bearing of the firstfeed passage, in that order. The second feed passage extends from thegear chamber to the return passage while bypassing the spiral passagewith the bypass passage. A portion of the lubricating oil flowing upwardfrom the gear mechanism flows through the bypass passage toward thereturn passage without passing through the spiral passage.

The bypass passage bypassing the spiral passage is thus provided in thesecond feed passage and, therefore, a flow rate of the lubricating oilflowing through a circulation path including the gear chamber, the feedpassage, the connection passage, and the return passage is notrestricted by the spiral passage. The lubricating oil is thus circulatedat a flow rate exceeding a supply capacity of the spiral passage.Circulation efficiency of the lubricating oil flowing through thecirculation path is thus improved and the lubricating oil inside thelower case is cooled effectively.

A flow passage area of the bypass passage may be greater or smaller thana flow passage area of the spiral passage, or may be equal to the flowpassage area of the spiral passage. In a case in which the flow passagearea of the bypass passage bypassing the spiral passage is greater thanthe flow passage area of the spiral passage, the lubricating oil isguided through the bypass passage at a flow rate greater than a flowrate of the lubricating oil flowing through the spiral passage. Thecirculation efficiency of the lubricating oil is thus improved.

The spiral passage preferably includes a spiral groove extending in theup/down direction while spirally surrounding the center line of thedriveshaft. At least a portion of the bypass passage is preferablylocated at a height between an upper end and a lower end of the spiralgroove. For example, both an upper end and a lower end of the bypasspassage may be located at heights between the upper end and the lowerend of the spiral groove. The spiral groove may be provided at an outerperipheral surface of the driveshaft or may be provided on a circular orsubstantially circular cylindrical surface surrounding the driveshaft.The circular cylindrical surface may be a portion of the lower case ormay be a portion of a member separate from the lower case.

The bypass passage may be integral and unitary with the lower case ormay be defined by a portion of a member separate from the lower case andheld by the lower case.

The connection passage preferably includes an upstream end connected tothe feed passage and a downstream end connected to the return passage.At least one of the upstream end and the downstream end of theconnection passage may be located above an oil surface of thelubricating oil when the prime mover is stopped.

The feed passage preferably includes a merging portion disposed on anupstream side of the connection passage and connecting the first feedpassage and the second feed passage to each other. The merging portionmay connect the first feed passage and the second feed passage to eachother either upstream or downstream of the upper bearing.

With the above structure, the first feed passage and the second feedpassage are connected to each other by the merging portion at a positionupstream of the connection passage and, therefore, excess lubricatingoil is released from one of the first feed passage and the second feedpassage to the other of the first feed passage and the second feedpassage. An increase in pressure of the lubricating oil at the firstfeed passage and the second feed passage is thus significantly reducedor prevented.

The merging portion preferably connects the first feed passage and thesecond feed passage to each other at a location that is upstream of theupper bearing and downstream of the spiral passage.

With the above structure, the lubricating oil that has bypassed thespiral passage is supplied from the second feed passage to the firstfeed passage at a location that is upstream of the upper bearing anddownstream of the spiral passage. The lubricating oil supplied to thefirst feed passage at the merging portion is supplied to an internal gapof the upper bearing that is located downstream of the merging portion.A flow rate of the lubricating oil supplied to the upper bearing is thusincreased. Further, the excess lubricating oil is released from thefirst feed passage to the second feed passage via the merging portion,so that the pressure of the lubricating oil is prevented from increasingat a portion between the upper bearing and the spiral passage.

The outboard motor preferably further includes a check valve disposedinside the second feed passage on an upstream side of the mergingportion and that prevents a reverse flow of the lubricating oil in whichthe lubricating oil inside the second feed passage flows toward the gearchamber.

With the above structure, if the lubricating oil to be supplied from thespiral passage to the interior of the upper bearing flows into thesecond feed passage via the merging portion, this lubricating oil isprevented from flowing in reverse inside the second feed passage. Thisdecreases the lubricating oil that flows from the spiral passage to thesecond feed passage via the merging portion, so that the lubricating oilis supplied from the spiral passage to the interior of the upper bearingat a sufficient flow rate, even if the prime mover rotates at low speed.

The second feed passage preferably extends from the gear chamber to thereturn passage via the connection passage. In this case, the second feedpassage may further include at least one outer peripheral passage thatbypasses the interior of the upper bearing. Preferably, a flow passagearea of the at least one outer peripheral passage is greater than theinternal gap of the upper bearing. Specifically, if the at least oneouter peripheral passage includes a plurality of outer peripheralpassages, a sum of flow passage areas of the plurality of outerperipheral passages is preferably greater than the internal gap of theupper bearing. If the at least one outer peripheral passage is a singleouter peripheral passage, the flow passage area of the outer peripheralpassage is preferably greater than the internal gap of the upperbearing.

With the above structure, the second feed passage extends toward theconnection passage while bypassing the internal gap of the upper bearingwith the outer peripheral passage. By bypassing the internal gap of theupper bearing that is small in flow passage area, a flow rate of thelubricating oil flowing through the second feed passage is preventedfrom being restricted by the internal gap of the upper bearing. Thecirculation efficiency of the lubricating oil is thus improved and thelubricating oil is cooled effectively.

A portion of the outer peripheral passage is preferably defined by anouter peripheral surface of the upper bearing.

With the above structure, an inner wall surface of the outer peripheralpassage that defines the outer peripheral passage includes the outerperipheral surface of the upper bearing, and the outer peripheralsurface of the upper bearing defines a portion of the outer peripheralpassage. The lubricating oil inside the outer peripheral passage flowswhile being in contact with the outer peripheral surface of the upperbearing. The upper bearing is thus cooled by the lubricating oil flowingthrough the outer peripheral passage. The upper bearing is thus cooledwhile improving the circulation efficiency of the lubricating oil.

The at least one outer peripheral passage preferably includes aplurality of outer peripheral passages spaced apart in thecircumferential direction of the driveshaft.

With the above structure, the second feed passage is provided with theplurality of outer peripheral passages that bypass the interior of theupper bearing. A flow passage area of the second feed passage is thusincreased and the circulation efficiency of the lubricating oil is thusimproved further.

The second feed passage preferably extends from the gear chamber to thereturn passage via the connection passage. In this case, the connectionpassage may include a first connection passage and a second connectionpassage that are different from each other. The first connection passageguides the lubricating oil from the first feed passage to the returnpassage and the second connection passage guides the lubricating oilfrom the second feed passage to the return passage.

With the above structure, the lubricating oil inside the first feedpassage is guided to the return passage by the first connection passageand the lubricating oil inside the second feed passage is guided to thereturn passage by the second connection passage. The first connectionpassage and the second connection passage are separate passages that donot intersect each other. A flow passage area of the connection passageis thus increased and the flow rate of the lubricating oil flowingthrough the circulation path is prevented from being restricted by theconnection passage.

The first feed passage is preferably connected to only the firstconnection passage and the second feed passage may be connected to onlythe second connection passage. Or, the second feed passage may beconnected to both the first connection passage and the second connectionpassage.

When the second feed passage is connected to both the first connectionpassage and the second connection passage, the second feed passageincludes a portion intersecting the first connection passage and aportion intersecting the second connection passage. When the amount oflubricating oil flowing through the second feed passage is high, aportion of the lubricating oil flows from the second feed passage to thesecond connection passage and the remaining lubricating oil flows fromthe second feed passage to the first connection passage. A portion ofthe lubricating oil flowing through the second feed passage is thusreleased to the first connection passage and the circulation flow rateof the lubricating oil is thus prevented from being restricted by thesecond connection passage.

The second feed passage preferably extends from the gear chamber to thereturn passage without passing through the connection passage.

With the above structure, the lubricating oil supplied from the gearchamber to the second feed passage flows into the return passage withoutpassing through the connection passage. The lubricating oil flowingupward from the gear mechanism is thus smoothly delivered from the gearchamber to the return passage. An increase in pressure of thelubricating oil at the second feed passage is thus significantly reducedor prevented.

In a case in which the second feed passage extends from the gear chamberto the return passage without passing through the connection passage,the bypass passage preferably extends obliquely downward from an innerwall surface of the return passage.

With the above structure, the bypass passage extends obliquely downwardfrom the inner wall surface of the return passage. The lubricating oilinside the bypass passage is guided obliquely upward to the returnpassage by the inner wall surface of the bypass passage. The gearmechanism sends upward the lubricating oil, so that the lubricating oilsupplied to the bypass passage has a velocity component in an upperdirection. A decrease of the velocity component of the lubricating oilis thus reduced when the lubricating oil is guided to the returnpassage. The lubricating oil flowing upward from the gear mechanism isthus smoothly delivered from the gear chamber to the return passagewhile bypassing the spiral passage.

The second feed passage preferably extends from the gear chamber to thereturn passage via the connection passage. In this case, the second feedpassage may be separate from the first feed passage at a region from anupstream end of the bypass passage to a location around the upperbearing. Or, the second feed passage may be separate from the first feedpassage at a region from the gear chamber to the location around theupper bearing.

With the above structure, the second feed passage is separate from thefirst feed passage until the second feed passage reaches the locationaround the upper bearing, so that the lubricating oil to be suppliedfrom the spiral passage to the interior of the upper bearing does notflow into the second feed passage. The lubricating oil is thus suppliedfrom the spiral passage to the interior of the upper bearing at asufficient flow rate, even if the prime mover rotates at low speed.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a left side of an outboard motor accordingto a first preferred embodiment of the present invention.

FIG. 2 is a vertical sectional view showing an interior of a lower caseprovided in the outboard motor.

FIG. 3 is a partially enlarged view of FIG. 2.

FIG. 4A is a view of a vertical section, including a center line of adriveshaft and perpendicular or substantially perpendicular to a centerline of a propeller shaft, as viewed from the rear.

FIG. 4B is a horizontal section taken along line B-B in FIG. 4A.

FIG. 4C is a horizontal section taken along line C-C in FIG. 4A.

FIG. 5 is a vertical sectional view showing an interior of a lower caseaccording to a second preferred embodiment of the present invention.

FIG. 6A is a sectional view showing an example of a check valve.

FIG. 6B is a sectional view showing an example of the check valve.

FIG. 7 is a vertical sectional view showing an interior of a lower caseaccording to a third preferred embodiment of the present invention.

FIG. 8 is a vertical sectional view showing an interior of a lower caseaccording to a fourth preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An outboard motor 2 in a reference orientation will be described below.The reference orientation is an orientation in which a rotational axisof a propeller shaft 7 extends horizontally in a front/rear direction.

FIG. 1 is a schematic view of a left side of an outboard motor 2according to a first preferred embodiment of the present invention. FIG.2 is a vertical sectional view showing an interior of a lower case 17provided in the outboard motor 2. FIGS. 1 and 2 show a state in whichthe outboard motor 2 is in the reference orientation.

As shown in FIG. 1, a vessel propulsion device 1 includes the outboardmotor 2 that generates a thrust that propels a vessel and a suspensionsystem mounting the outboard motor 2 to a hull H1.

The outboard motor 2 includes a prime mover 3 that generates motivepower to rotate a propeller 8, and a power transmission that transmitsthe motive power of the prime mover 3 to the propeller 8. Rotation ofthe prime mover 3 is transmitted to the propeller 8 via a driveshaft 5,a gear mechanism 6, and a propeller shaft 7 of the power transmission.The propeller 8 is thus made to rotate together with the propeller shaft7 to generate a thrust that propels a vessel forward or rearward.

The suspension system includes a pair of clamp brackets 9, fixed to atransom provided at a rear portion of the hull H1, and a tilting shaft10, supported by the pair of clamp brackets 9 in an orientationextending horizontally in the right/left direction. The suspensionsystem further includes a swivel bracket 11, supported by the pair ofclamp brackets 9 via the tilting shaft 10, and a steering shaft 12,supported by the swivel bracket 11 in an orientation extendingvertically in an up/down direction.

The outboard motor 2 is coupled to an upper end and a lower end of thesteering shaft 12. The steering shaft 12 is rotatable with respect tothe swivel bracket 11 around a center line of the steering shaft 12 thatextends in the up/down direction. The swivel bracket 11 is rotatablewith respect to the clamp brackets 9 around a center line of the tiltingshaft 10 that extends in the right/left direction. The outboard motor 2is rotatable in the right/left direction with respect to the hull H1 andis rotatable in the up/down direction with respect to the hull H1.

The vessel propulsion device 1 includes a steering mechanism that pivotsthe outboard motor 2 around the steering shaft 12 with respect to theclamp brackets 9, and a power trim and tilt mechanism (hereinafterreferred to as “PTT”) that pivots the outboard motor 2 around thetilting shaft 10 with respect to the clamp brackets 9. A hydrauliccylinder 13 of the PTT is disposed between the pair of clamp brackets 9.The PTT positions the outboard motor 2 at any position from a tilt-downposition (position shown in FIG. 1) at which the propeller 8 ispositioned underwater to a tilt-up position at which the propeller 8 ispositioned above a water surface.

The outboard motor 2 includes a cowling 14 that houses the prime mover 3and a casing that houses the power transmission. The casing includes anexhaust guide 15 disposed below the prime mover 3, an upper case 16disposed below the exhaust guide 15, and a lower case 17 disposed belowthe upper case 16. The lower case 17 includes a circular orsubstantially circular cylindrical torpedo portion 17 a extending in thefront/rear direction. The torpedo portion 17 a is a portion that isdisposed underwater. The torpedo portion 17 a includes a closed frontend, a rearwardly open rear end, and a tapered outer surface thatnarrows as the front end is approached.

The driveshaft 5 extends in the up/down direction inside the exhaustguide 15, the upper case 16, and the lower case 17. The gear mechanism 6is coupled to a lower end of the driveshaft 5. The propeller shaft 7extends in the front/rear direction inside the torpedo portion 17 a. Thegear mechanism 6 is coupled to a front end of the propeller shaft 7. Thepropeller 8 is removably mounted to a rear end of the propeller shaft 7that projects rearward from a rear end of the torpedo portion 17 a. Thedriveshaft 5 is rotatable with respect to the casing around a centerline (drive axis Ad) of the driveshaft 5. The propeller shaft 7 isrotatable with respect to the casing around a center line (propelleraxis Ap) of the propeller shaft 7.

The prime mover 3 includes an engine, for example, an internalcombustion engine. The prime mover 3 may include an electric motor ormay include both an engine and an electric motor. A rear end of thepropeller 8 defines an exhaust port 19 that discharges exhaust gasunderwater. The exhaust gas generated in the prime mover 3 is dischargedunderwater from the exhaust port 19 via an exhaust passage 18 providedin an interior of the outboard motor 2. The prime mover 3 is disposed onthe exhaust guide 15 that defines a prime mover support in anorientation in which the rotational axis Ac of the crankshaft 4 isvertical or substantially vertical. A direction of the rotationtransmitted from the driveshaft 5 to the propeller shaft 7 is switchedby the gear mechanism 6. The propeller 8 rotates in the same directionas the propeller shaft 7. A direction of rotation of the propeller 8 isthus switched between a forward rotation direction and a reverserotation direction. A direction of the thrust is thus switched.

As shown in FIG. 2, the gear mechanism 6 includes a cylindrical orsubstantially cylindrical pinion 21 that rotates around the drive axisAd together with the driveshaft 5, a cylindrical or substantiallycylindrical front gear 22 and rear gear 23 engaged with the pinion 21,and a cylindrical or substantially cylindrical dog clutch 24 thatselectively engages with one of the front gear 22 and the rear gear 23.The outboard motor 2 includes a shift mechanism that moves the dogclutch 24 in an axial direction (front/rear direction) of the propellershaft 7 to switch a shift state of the gear mechanism 6.

The pinion 21 is coupled to a lower end of the driveshaft 5. Thedriveshaft 5 is inserted in a shaft insertion hole 25 provided in thelower case 17. The driveshaft 5 is rotatably supported by the lower case17 via an upper bearing B1 and a lower bearing B2 that surround thedriveshaft 5. The pinion 21 is disposed below the lower bearing B2, andthe upper bearing B1 is disposed above the lower bearing B2.

Each of the upper bearing B1 and the lower bearing B2 may include any ofa ball bearing, a roller bearing, and a needle bearing, for example.FIG. 2 shows an example in which the upper bearing B1 is a double-rowtapered roller bearing and the lower bearing B2 is a needle bearing. Theupper bearing B1 includes an inner ring surrounding the driveshaft 5, anouter ring surrounding the inner ring, and a plurality of rollersinterposed between the inner ring and the outer ring. The lower bearingB2 includes an outer ring surrounding the driveshaft 5 and a pluralityof needles interposed between the outer ring and the driveshaft 5.

The inner ring of the upper bearing B1 is sandwiched in an axialdirection of the driveshaft 5 by an annular nut 26 mounted to thedriveshaft 5 and an annular step portion provided in the driveshaft 5.The outer ring of the upper bearing B1 is sandwiched in the axialdirection of the driveshaft 5 by an annular fixing ring 27 mounted to aninner peripheral surface of the shaft insertion hole 25 and an annularstep portion provided at the shaft insertion hole 25. The fixing ring 27surrounds a nut 26 across an interval in a radial direction of thedriveshaft 5. The nut 26 and the fixing ring 27 are located between theupper bearing B1 and a shaft cap 28. An upper end of the shaft insertionhole 25 is closed by the cylindrical shaft cap 28 that surrounds thedriveshaft 5.

The front gear 22 is disposed farther to the front than the drive axisAd. The rear gear 23 is disposed farther to the rear than the drive axisAd. The dog clutch 24 is disposed between the front gear 22 and the reargear 23. A front end of the propeller shaft 7 is inserted inside thecylindrical front gear 22, rear gear 23, and dog clutch 24. The frontgear 22 and the rear gear 23 are supported by the lower case 17 so as tobe rotatable around the propeller axis Ap. When the prime mover 3rotates the driveshaft 5, the rotation of the pinion 21 defining a drivegear is transmitted to the front gear 22 and the rear gear 23 definingdriven gears, and the front gear 22 and the rear gear 23 rotate inmutually opposite directions.

The front gear 22 is rotatably supported by the lower case 17 via afront bearing B3 that surrounds the front gear 22. The rear gear 23 isrotatably supported by the lower case 17 via a rear bearing B4 thatsurrounds the rear gear 23. The front bearing B3 is inserted inside thetorpedo portion 17 a, and the rear bearing B4 is inserted inside acylindrical or substantially cylindrical bearing housing 29 surroundingthe propeller shaft 7. The rear bearing B4 is supported by the lowercase 17 via the bearing housing 29.

The dog clutch 24 is spline coupled to the propeller shaft 7. The dogclutch 24 is movable in an axial direction of the propeller shaft 7 withrespect to the propeller shaft 7 and rotates integrally with thepropeller shaft 7 around the propeller axis Ap. The dog clutch 24includes a front engaging portion 24 a facing an engaging portion of thefront gear 22 and a rear engaging portion 24 b facing an engagingportion of the rear gear 23. The dog clutch 24 is movable along thepropeller shaft 7 in the front/rear direction between a forward rotationposition at which the front engaging portion 24 a engages with theengaging portion of the front gear 22 and a reverse rotation position atwhich the rear engaging portion 24 b engages with the engaging portionof the rear gear 23. A position between the forward rotation positionand the reverse rotation position is a neutral position (position shownin FIG. 2) at which the dog clutch 24 is not engaged with either of thefront gear 22 and the rear gear 23.

The pinion 21, the front gear 22, the rear gear 23, and the dog clutch24 are disposed inside a gear chamber 30 provided in the torpedo portion17 a. The gear chamber 30 is defined by an inner surface of the torpedoportion 17 a. The gear chamber 30 is filled with a lubricating oil (gearoil) that lubricates the gear mechanism 6. The shaft insertion hole 25is disposed above the gear chamber 30. The shaft insertion hole 25 isconnected to the gear chamber 30 via a lower bearing bypass groove 57provided around the lower bearing B2. The lubricating oil is movablebetween the gear chamber 30 and the shaft insertion hole 25 via thelower bearing bypass groove 57.

The shift mechanism positions the dog clutch 24 at one shift positionamong the forward rotation position, the reverse rotation position, andthe neutral position. The shift mechanism includes a shift actuator 31(see FIG. 1) driven in accordance with a shift operation by a user and ashift rod 32 that is driven to rotate by the shift actuator 31. Theshift mechanism further includes a slide shaft 33 driven in thefront/rear direction by the shift rod 32 and a coupling pin 34 couplingthe slide shaft 33 and the dog clutch 24.

The shift rod 32 includes a rod portion 32 a extending in the up/downdirection, a disk portion 32 b disposed below the rod portion 32 a, anda crank portion 32 c disposed below the disk portion 32 b. The rodportion 32 a and the disk portion 32 b are coaxial and a portion(eccentric portion) of the crank portion 32 c is eccentric with respectto the rod portion 32 a and the disk portion 32 b. An outer diameter ofthe disk portion 32 b is greater than an outer diameter of the rodportion 32 a.

The rod portion 32 a is located in front of the driveshaft 5 and isparallel or substantially parallel to the driveshaft 5. The rod portion32 a is inserted in a rod insertion hole 36 provided at the lower case17. The rod insertion hole 36 extends in the up/down direction along therod portion 32 a. An inner peripheral surface of the rod insertion hole36 surrounds the rod portion 32 a across an interval in a radialdirection of the shift rod 32. The rod portion 32 a projects upward froman upper end of the rod insertion hole 36. The upper end of the rodinsertion hole 36 is closed by an annular rod cap 35 that surrounds therod portion 32 a. A lower end of the rod insertion hole 36 is closed bythe disk portion 32 b. The rod portion 32 a is supported by the lowercase 17 via the rod cap 35 so as to be rotatable around a center line ofthe rod portion 32 a.

The inner peripheral surface of the rod insertion hole 36, the rod cap35, and the disk portion 32 b define a shift chamber 37 that houses therod portion 32 a. The shift chamber 37 is located above the gear chamber30. The shift chamber 37 is connected to the gear chamber 30 via aplurality of rod bypass grooves 38 disposed around the disk portion 32b. The shift chamber 37 is also connected to the gear chamber 30 via apenetrating hole 39 that penetrates through a portion of the lower case17, located between the shift rod 32 and the pinion 21, in thefront/rear direction. The penetrating hole 39 is located between theshift rod 32 and the pinion 21. The lubricating oil is movable betweenthe gear chamber 30 and the shift chamber 37 via the rod bypass grooves38 or the penetrating hole 39.

The lubricating oil that lubricates the gears, bearings, etc., is storednot only in the gear chamber 30 but also in the shaft insertion hole 25and the shift chamber 37. The gear chamber 30, the shaft insertion hole25, and the shift chamber 37 define an oil storage chamber that storesthe lubricating oil. When the prime mover 3 is stopped and idle, an oilsurface (oil level L1) of the lubricating oil is located between anupper end of the upper bearing B1 and a lower end of the upper bearingB1. That is, the entire gear chamber 30 is filled with the lubricatingoil and portions of the shaft insertion hole 25 and the shift chamber 37are filled with the lubricating oil. A location (height) of the oilsurface of the lubricating oil changes in accordance with a temperatureof the lubricating oil.

The slide shaft 33 includes a front shaft 33 a mounted to the crankportion 32 c and a rear shaft 33 b mounted to the coupling pin 34. Therear shaft 33 b is inserted inside the propeller shaft 7 from the frontof the propeller shaft 7, and the front shaft 33 a extends forward fromthe rear shaft 33 b. The front shaft 33 a projects forward from a frontend of the propeller shaft 7. The crank portion 32 c is mounted to thefront shaft 33 a at the front of the propeller shaft 7.

When the user operates a shift lever provided in a vessel operatorcompartment, the shift actuator 31 (see FIG. 1) causes the shift rod 32to pivot around the center line of the rod portion 32 a. A portion ofthe crank portion 32 c is eccentric with respect to the rod portion 32 aand therefore when the shift rod 32 pivots, a portion of the crankportion 32 c moves in the front/rear direction. The front shaft 33 a isthus pushed forward or rearward by the crank portion 32 c and moves inthe front/rear direction. Accordingly, the rear shaft 33 b, the couplingpin 34, and the dog clutch 24 move integrally in the front/reardirection. The dog clutch 24 is thus disposed at one of the forwardrotation position, the reverse rotation position, and the neutralposition.

The outboard motor 2 includes a water cooling apparatus that coolsrespective portions of the outboard motor 2 including the prime mover 3.The water cooling apparatus includes a first water inlet 41 and a secondwater inlet 42 that opens at an outer surface of the outboard motor 2, acooling water passage that guides the water outside the outboard motor 2that flowed into the first water inlet 41 and the second water inlet 42to the respective portions of the outboard motor 2, and a water pump 45that generates a suction force that suctions the water outside theoutboard motor 2 into the first water inlet 41 and the second waterinlet 42.

The water pump 45 that is driven by the prime mover 3 is disposed on thecooling water passage provided in an interior of the outboard motor 2.The cooling water passage includes a first water supply passage 43 and asecond water supply passage 44, which guide the water outside theoutboard motor 2 to the respective portions of the outboard motor 2, anda drain passage by which the water that has cooled the respectiveportions of the outboard motor 2 is discharged to outside the outboardmotor 2. The first water supply passage 43 extends to the water pump 45from the first water inlet 41, disposed farther to the front than thedriveshaft 5, and the second water supply passage 44 extends to thewater pump 45 from the second water inlet 42, disposed farther to therear than the driveshaft 5.

The water pump 45 includes an impeller 45 a that rotates together withthe driveshaft 5 and a pump case 45 b that houses the impeller 45 a.When the prime mover 3 rotates the driveshaft 5, the impeller 45 arotates with respect to the pump case 45 b. The pump case 45 b isconnected to the first water inlet 41 and the second water inlet 42 viathe first water supply passage 43 and the second water supply passage 44provided at the lower case 17. When the prime mover 3 rotates thedriveshaft 5, the water outside the outboard motor 2 is suctioned ascooling water from the first water inlet 41 and the second water inlet42 and via the first water supply passage 43 and the second water supplypassage 44 into an interior of the pump case 45 b and fed to the primemover 3, etc., from the pump case 45. The respective portions of theoutboard motor 2 are thus cooled.

The oil storage chamber that includes the gear chamber 30, the shaftinsertion hole 25, and the shift chamber 37 is provided at the lowercase 17 that is disposed underwater. The lower case 17 is preferablymade of a metal that is higher in thermal conductivity than a resin. Thelubricating oil inside the oil storage chamber is thus cooled by thewater outside the outboard motor 2. Further, just a first partition wall17 x of the lower case 17 is interposed between the first water supplypassage 43 and the shift chamber 37 and just a second partition wall 17f lower case 17 is interposed between the second water supply passage 44and the shaft insertion hole 25. The lubricating oil inside the shiftchamber 37 and the shaft insertion hole 25 are thus cooled effectivelyby the cooling water flowing through the first water supply passage 43and the second water supply passage 44.

An oil circulation system that circulates the lubricating oil inside theoutboard motor 2 will now be described.

FIG. 3 is partially enlarged view of FIG. 2. FIG. 4A is a view of avertical section, including the drive axis Ad that is perpendicular orsubstantially perpendicular to the propeller axis Ap, as viewed from therear. FIG. 4B is a horizontal section taken along line B-B in FIG. 4A,and FIG. 4C is a horizontal section taken along line C-C in FIG. 4A.

As shown in FIG. 3, the oil circulation system includes a feed passage51, 52 that feeds the lubricating oil upward from the gear chamber 30, areturn passage 55 that returns the lubricating oil, fed by the feedpassage, to the gear chamber 30, and a connection passage 53, 54 thatguides the lubricating oil from the feed passage to the return passage55.

The feed passage includes a first feed passage 51 and a second feedpassage 52 that are separate from each other between the upper bearingB1 and the lower bearing B2. The return passage 55 is defined by theshift chamber 37 and the plurality of rod bypass grooves 38. Theconnection passage includes one or more passages extending from the feedpassage to the return passage 55. FIG. 3 shows an example in which theconnection passage is provided with a first connection passage 53 and asecond connection passage 54.

The gear chamber 30, the feed passage, the connection passage, and thereturn passage 55 define a circulation path through which thelubricating oil inside the lower case 17 is circulated. When the primemover 3 rotates the driveshaft 5, the lubricating oil inside the gearchamber 30 is fed upward due to rotation of the gear mechanism 6 and thelubricating oil is fed upward by a screw pump defined by a spiral groove59 and a pump defining surface 60. The lubricating oil inside the gearchamber 30 is thus made to pass through the feed passage, the connectionpassage, and the return passage 55, in that order, and return to thegear chamber 30. In this process, the lubricating oil is cooled by thelower case 17, etc.

The first feed passage 51 includes a first upstream passage 56 extendingupward from the gear chamber 30, a spiral passage 58 provided around thedriveshaft 5, an internal gap of the upper bearing B1, and a firstdownstream passage 61 provided between the upper bearing B1 and theshaft cap 28. The internal gap of the upper bearing B1 is, for example,a gap between the inner ring and the outer ring of the upper bearing B1.The spiral passage 58 is an example of a first intermediate passage.

The second feed passage 52 includes a second upstream passage extendingupward from the gear chamber 30, a bypass passage 62 separate from thespiral passage 58 by a portion of the lower case 17, and one or moreouter peripheral passages 63 extending upward from the bypass passage 62while bypassing an interior of the upper bearing B1. FIG. 3 shows anexample in which two outer peripheral passages 63 are provided and thesecond upstream passage is the same passage as the first upstreampassage 56. The bypass passage 62 is an example of a second intermediatepassage, and each outer peripheral passage 63 is an example of a seconddownstream passage.

The first upstream passage 56 is, for example, located in front of thelower bearing B2. An upstream end of the first upstream passage 56 thatcorresponds to a lower end is located lower than the lower bearing B2and faces an engaging portion of the pinion 21 and the front gear 22 inthe up/down direction. A downstream end of the first upstream passage 56that corresponds to an upper end is located above the lower bearing B2and faces an outer peripheral surface of the driveshaft 5 in a radialdirection. As long as it extends upward from the gear chamber 30, thefirst upstream passage 56 may be vertical or may be inclined.

The first upstream passage 56 is defined by an inner surface of thelower bearing bypass groove 57 provided at the lower case 17 and anouter peripheral surface of the lower bearing B2. The lower bearingbypass groove 57 extends in the up/down direction along the outerperipheral surface of the lower bearing B2. The lower bearing bypassgroove 57 is recessed outward from a circular or substantially circularcylindrical surface in contact with an outer peripheral surface of theouter ring of the lower bearing B2. A flow passage area of the firstupstream passage 56 is greater than a flow passage area of the spiralpassage 58.

The spiral passage 58 extends in the up/down direction along thedriveshaft 5 while spirally surrounding the driveshaft 5. The spiralpassage 58 includes the spiral groove 59 provided on an outer peripheralsurface of a groove defining portion 5 a of the driveshaft 5 and thecircular cylindrical pump defining surface 60, which is a portion of theinner peripheral surface of the shaft insertion hole 25. The spiralgroove 59 and the pump defining surface 60 define the screw pump thatfeeds the lubricating oil upward due to the rotation of the driveshaft5. A rotation direction of the spiral groove 59 is set so that thelubricating oil is fed upward in along with the rotation of thedriveshaft 5. If the rotation direction of the driveshaft 5 is, forexample, clockwise as viewed from above, the spiral groove 59 extendsclockwise as viewed from above.

The spiral groove 59 extends in the up/down direction while spirallysurrounding the center line of the driveshaft 5. An upper end of thespiral groove 59 corresponds to a downstream end of the spiral passage58 and a lower end of the spiral groove 59 corresponds to an upstreamend of the spiral passage 58. The upper end and the lower end of thespiral groove 59 are located at heights between the lower end of theupper bearing B1 and the upper end of the lower bearing B2. The lowerend of the spiral groove 59 is located at the same height as thedownstream end of the first upstream passage 56.

The first downstream passage 61 extends upward from the upper bearingB1. The first downstream passage 61 is in communication with theinternal gap of the upper bearing B1. The first downstream passage 61guides the lubricating oil, which has passed upward through the internalgap of the upper bearing B1, toward the first connection passage 53. Thefirst downstream passage 61 is located between the upper bearing B1 andthe shaft cap 28. The first downstream passage 61 passes between anouter peripheral surface of the nut 26 and an inner peripheral surfaceof the fixing ring 27 and extends from the upper bearing B1 to the shaftcap 28.

The bypass passage 62 extends upward from the first upstream passage 56.The bypass passage 62 is located below the upper bearing B1. The bypasspassage 62 is located in front of the driveshaft 5. The bypass passage62 is located between the shaft insertion hole 25 and the shaft chamber37. The bypass passage 62 includes the lower case 17 and is integral andunitary with the lower case 17.

The bypass passage 62 is a separate passage from the spiral passage 58and does not intersect the spiral passage 58. A flow passage area of thebypass passage 62 is greater than the flow passage area of the spiralpassage 58. In a radial direction of the driveshaft 5, the bypasspassage 62 is located farther outward than the spiral passage 58. Thebypass passage 62 is separate from the spiral passage 58 by a partitionwall 17 z of the lower case 17. The partition wall 17 z is locatedbetween the spiral passage 58 and the bypass passage 62 in the radialdirection of the driveshaft 5.

An upper end of the bypass passage 62 corresponds to a downstream end ofthe bypass passage 62, and a lower end of the bypass passage 62corresponds to an upstream end of the bypass passage 62. Both the upperend and the lower end of the bypass passage 62 are located at heightsbetween the upper end and the lower end of the spiral groove 59. Thebypass passage 62 may be vertical from its upper end to its lower end ormay be inclined obliquely with respect to a vertical direction. Also,the bypass passage 62 may have a broken line shape or a curved shape. Alength of the bypass passage 62 in the up/down direction is shorter thana distance in the up/down direction from the lower end of the upperbearing B1 to the upper end of the lower bearing B2 and is longer thanan outer diameter of the upper bearing B1.

As shown in FIG. 4A, the bypass passage 62 is longer than the firstupstream passage 56 and the outer peripheral passages 63 in the up/downdirection. As shown in FIG. 4B and FIG. 4C, the bypass passage 62preferably is provided only in an annular region surrounding the pumpdefining surface 60. The bypass passage 62 preferably has, for example,a horizontal cross section of a circular shape. As shown in FIG. 4C, aninner diameter D2 of the bypass passage 62 is less than an outerdiameter D1 of the groove defining portion 5 a, which is a maximum valueof the outer diameter of the driveshaft 5.

As shown in FIG. 3, each outer peripheral passage 63 extends in theup/down direction along an outer peripheral surface of the upper bearingB1. Each outer peripheral passage 63 is longer than the upper bearing B1in the up/down direction. The plurality of outer peripheral passages 63include a front outer peripheral passage 63 f located in front of theupper bearing B1 and a lateral outer peripheral passage 63L locatedlaterally of the upper bearing B1. The plurality of outer peripheralpassages 63 are disposed across an interval in a circumferentialdirection of the driveshaft 5. The outer peripheral passages 63 aredefined by an inner surface of an upper bearing bypass groove 64provided at the lower case 17 and the outer peripheral surface of theupper bearing B1.

Upper ends of the outer peripheral passages 63 that correspond todownstream ends are located at heights between the upper end of theupper bearing B1 and a lower end of the rod cap 35. The upper ends ofthe outer peripheral passages 63 are disposed around the fixing ring 27.Lower ends of the outer peripheral passages 63 that correspond toupstream ends are located at heights between the upper end of the bypasspassage 62 and the lower end of the upper bearing B1. The outerperipheral passages 63 are connected to the first feed passage 51 via amerging portion 65 located at a height between the upper end of thebypass passage 62 and the lower end of the upper bearing B1. The mergingportion 65 faces the outer peripheral surface of the driveshaft 5 acrossan interval in a radial direction.

The first connection passage 53 and the second connection passage 54 areseparate passages that do not intersect each other. The first connectionpassage 53 and the second connection passage 54 are parallel orsubstantially parallel to each other and extend obliquely downward fromthe shaft insertion hole 25 to the shift chamber 37. The firstconnection passage 53 and the second connection passage 54 are locatedat heights between an upper end 25 a of the shaft insertion hole 25 andthe lower end of the upper bearing B1. The first connection passage 53is located above the second connection passage 54. The second connectionpassage 54 is located lower than the nut 26 and the fixing ring 27. Thefirst connection passage 53 and the second connection passage 54mutually overlap in plan view.

An upstream end of the first connection passage 53 opens at the innerperipheral surface of the shaft insertion hole 25. An upstream end ofthe second connection passage 54 opens at an inner peripheral surface ofthe upper bearing bypass groove 64. Downstream ends of both the firstconnection passage 53 and the second connection passage 54 open at aninner surface of the shift chamber 37. When the prime mover 3 isstopped, both the upstream end and the downstream end of the firstconnection passage 53 are disposed higher than the oil surface (oillevel L1) of the lubricating oil. A length of the first connectionpassage 53, that is, a length of a center line of the first connectionpassage 53 is shorter than the outer diameter of the upper bearing B1and longer than an inner diameter of the first connection passage 53.The same applies to the second connection passage 54.

An upper portion of the upstream end of the first connection passage 53is located higher than the fixing ring 27 and is disposed at the sameheight as the first downstream passage 61. A lower portion of theupstream end of the first connection passage 53 is disposed around thefixing ring 27 and is disposed at the same height as the upper ends ofthe outer peripheral passages 63. The upstream end of the secondconnection passage 54 is disposed around the upper bearing B1 and facesthe outer peripheral surface of the upper bearing B1 across an intervalin a radial direction. The second connection passage 54 is directlyconnected to the outer peripheral passage 63. The first connectionpassage 53 is directly connected to each of the first downstream passage61 and the outer peripheral passage 63. The second connection passage 54is indirectly connected to the first downstream passage 61 and the firstconnection passage 53 via the outer peripheral passage 63.

A flow of the lubricating oil inside the lower case 17 will now bedescribed with reference to FIG. 3.

When the prime mover 3 (see FIG. 1) rotates the driveshaft 5, the pinion21, the front gear 22, and rear gear 23 rotate around their respectivecenter lines, and the spiral groove 59 provided at the groove definingportion 5 a of the driveshaft 5 a rotates around the drive axis Ad. Atthe same time, the water pump 45 rotates and the water outside theoutboard motor 2 is supplied as cooling water to the water pump 45 viathe first water supply passage 43 and the second water supply passage44.

The gear chamber 30, in which the pinion 21, the front gear 22, and therear gear 23 are housed, is filled with the lubricating oil. When thefront gear 22 rotates, the lubricating oil inside the gear chamber 30flows upward from the front gear 22 and is supplied to the firstupstream passage 56 shared by the first feed passage 51 and the secondfeed passage 52. A portion of the lubricating oil supplied to the firstupstream passage 56 is fed upward along the spiral passage 58 by thescrew pump defined by the spiral groove 59 and the pump defining surface60. The remaining lubricating oil supplied to the first upstream passage56 is guided upward by the bypass passage 62.

The lubricating oil guided upward by the spiral passage 58 is suppliedto the internal gap of the upper bearing B1. A portion of thelubricating oil guided upward by the bypass passage 62 is supplied tothe first feed passage 51 via the merging portion 65 and the remaininglubricating oil is supplied to the front outer peripheral passage 63 flocated in front of the upper bearing B1. A portion of the lubricatingoil supplied to the first feed passage 51 via the merging portion 65 issupplied to the internal gap of the upper bearing B1 and the remaininglubricating oil is supplied to the lateral outer peripheral passage 63Llocated on a lateral side of the upper bearing B1.

The lubricating oil guided by the front outer peripheral passage 63 f issupplied to the second connection passage 54 disposed below the firstconnection passage 53. Also, the lubricating oil guided by the lateralouter peripheral passage 63L is supplied to the first downstream passage61 located above the upper bearing B1. The lubricating oil dischargedupward from the internal gap of the upper bearing B1 is also supplied tothe first downstream passage 61. The lubricating oil supplied to thefirst downstream passage 61 is supplied to the first connection passage53.

The first downstream passage 61 is connected not just to the firstconnection passage 53 but also to the second connection passage 54 viathe front outer peripheral passage 63 f. When a pressure of thelubricating oil at the first downstream passage 61 is higher than apressure of the lubricating oil at the front outer peripheral passage 63f, a portion of the lubricating oil inside the first downstream passage61 flows into the first connection passage 53 and the remaininglubricating oil is supplied to the second connection passage 54 afterflowing in reverse through the front outer peripheral passage 63 f.Oppositely, when the pressure of the lubricating oil at the firstdownstream passage 61 is lower than the pressure of the lubricating oilat the front outer peripheral passage 63 f, a portion of the lubricatingoil inside the front outer peripheral passage 63 f flows into the secondconnection passage 54 and the remaining lubricating oil is supplied tothe first connection passage 53.

The lubricating oil supplied to the first connection passage 53 and thesecond connection passage 54 is guided from the shaft insertion hole 25of the feed passage to the rod insertion hole 36 of the return passage55. The lubricating oil supplied inside the rod insertion hole 36 flowsdownward inside the rod insertion hole 36 due to gravity while beingcooled by the lower case 17. The lubricating oil that has reached avicinity of the disk portion 32 b of the shift rod 32 flows into thegear chamber 30 via the rod bypass groove 38. The lubricating oil isthus returned to the gear chamber 30 by the return passage 55. Thelubricating oil that has returned to the gear chamber 30 is fed upwardagain by the rotation of the gear mechanism 6.

As described above, with the present preferred embodiment, when theprime mover 3 rotates the driveshaft 5, the gear mechanism 6 housed inthe gear chamber 30 of the lower case 17 rotates and the lubricating oilinside the gear chamber 30 is fed upward. The lubricating oil is thusmade to flow through the first upstream passage 56, the spiral passage58, and the upper bearing B1 interior of the first feed passage 51, inthat order. The second feed passage 52 extends from the first upstreampassage 56 to the connection passage while bypassing the spiral passage58 with the bypass passage 62. A portion of the lubricating oil flowingupward from the gear mechanism 6 flows through the bypass passage 62toward the connection passage without passing through the spiral passage58.

The bypass passage 62 that bypasses the spiral passage 58 is thusprovided in the second feed passage 52 and therefore a flow rate of thelubricating oil flowing through the circulation path including the gearchamber 30, the feed passage, the connection passage, and the returnpassage 55 is not restricted by the spiral passage 58. The lubricatingoil is thus circulated at a flow rate exceeding a supply capacity of thespiral passage 58. Circulation efficiency of the lubricating oil flowingthrough the circulation path is thus improved and the lubricating oilinside the lower case 17 is cooled effectively.

Further, the lubricating oil is released to the bypass passage 62, sothat the lubricating oil is prevented from increasing in pressure at thefirst upstream passage 56, even if a flow rate of the lubricating oilflowing upward from the gear mechanism 6 increases. Further, the bypasspassage 62 is not provided inward of the spiral passage 58 but isprovided outward of the spiral passage 58, so that complicating thestructure of the passage is prevented. Moreover, the diameter D2 of thecross section of the bypass passage 62 is smaller than the maximumdiameter D1 of the driveshaft 5, so that an increase in size of thelower case 17 is prevented.

With the present preferred embodiment, the flow passage area of thebypass passage 62 bypassing the spiral passage 58 is greater than theflow passage area of the spiral passage 58. The lubricating oil is thusguided through the bypass passage 62 at a flow rate greater than a flowrate of the lubricating oil flowing through the spiral passage 58. Thecirculation efficiency of the lubricating oil is thus improved.

With the present preferred embodiment, the first feed passage 51 and thesecond feed passage 52 are connected to each other by the mergingportion 65 at a location upstream of the connection passage andtherefore excess lubricating oil is released from one of the first feedpassage 51 and the second feed passage 52 to the other of the first feedpassage 51 and the second feed passage 52. A pressure increase of thelubricating oil at the first feed passage 51 and the second feed passage52 is thus significantly reduced or prevented.

With the present preferred embodiment, the lubricating oil that hasbypassed the spiral passage 58 is supplied from the second feed passage52 to the first feed passage 51 at a location that is upstream of theupper bearing B1 and downstream of the spiral passage 58. Thelubricating oil supplied to the first feed passage 51 at the mergingportion 65 is supplied to the internal gap of the upper bearing B1 thatis located downstream of the merging portion 65. The flow rate of thelubricating oil supplied to the upper bearing B1 is thus increased.Further, the excess lubricating oil is released from the first feedpassage 51 to the second feed passage 52 via the merging portion 65, sothat the pressure of the lubricating oil is prevented from increasing ata portion between the upper bearing B1 and the spiral passage 58.

With the present preferred embodiment, the second feed passage 52extends toward the connection passage while bypassing the internal gapof the upper bearing B1 with the plurality of outer peripheral passages63. By bypassing the internal gap of the upper bearing B1 that is smallin flow passage area, the flow rate of the lubricating oil flowingthrough the second feed passage 52 is prevented from being restricted bythe internal gap of the upper bearing B1. Further, the second feedpassage 52 is provided with the plurality of outer peripheral passages63, so that a sufficient flow passage area is secured for the passagebypassing the upper bearing B1.

With the present preferred embodiment, an inner wall surface of eachouter peripheral passage 63 includes the outer peripheral surface of theupper bearing B1, and the outer peripheral surface of the upper bearingB1 defines portions of the outer peripheral passage. The lubricating oilinside each outer peripheral passage 63 flows while in contact with theouter peripheral surface of the upper bearing B1. The upper bearing B1is thus cooled by the lubricating oil flowing through each outerperipheral passage 63. The upper bearing B1 is thus cooled whileimproving the circulation efficiency of the lubricating oil.

With the present preferred embodiment, the lubricating oil inside thefirst feed passage 51 is guided to the return passage 55 by the firstconnection passage 53 and the lubricating oil inside the second feedpassage 52 is guided to the return passage 55 by the second connectionpassage 54. The first connection passage 53 and the second connectionpassage 54 are separate passages that do not intersect each other. Aflow passage area of the connection passage is thus increased and theflow rate of the lubricating oil flowing through the circulation path isprevented from being restricted by the connection passage.

With the present preferred embodiment, the second feed passage 52 isconnected not just to the second connection passage 54 but also to thefirst connection passage 53. The second feed passage 52 includes aportion intersecting the first connection passage 53 and a portionintersecting the second connection passage 54. When the amount oflubricating oil flowing through the second feed passage 52 is high, aportion of the lubricating oil flows from the second feed passage 52 tothe second connection passage 54 and the remaining lubricating oil flowsfrom the second feed passage 52 to the first connection passage 53. Aportion of the lubricating oil flowing through the second feed passage52 is thus released to the first connection passage 53 and thecirculation flow rate of the lubricating oil is thus prevented frombeing restricted by the second connection passage 54.

Second Preferred Embodiment

A second preferred embodiment of the present invention will be describedbelow. A main difference of the second preferred embodiment with respectto the first preferred embodiment is that a check valve 271 is providedin the second feed passage 52 and the check valve 271 prevents a reverseflow of the lubricating oil.

FIG. 5 is a vertical sectional view showing the interior of the lowercase 17 according to the second preferred embodiment of the presentinvention. FIGS. 6A and 6B are sectional views showing examples of thecheck valve 271. In FIG. 5, FIG. 6A, and FIG. 6B, components equivalentto the components shown in FIG. 1 to FIG. 4C are denoted by the samereference numerals as in FIG. 1, etc., and description thereof will beomitted.

The check valve 271 is disposed inside the second feed passage 52 on anupstream side of the merging portion 65. FIG. 5 shows an example inwhich the check valve 271 is disposed inside the bypass passage 62. Aportion or an entirety of the check valve 271 is disposed above anintermediate height L2 between the upper bearing B1 and the lowerbearing B2, for example. The check valve 271 preferably is disposedclose to the merging portion 65.

The check valve 271 allows the lubricating oil to pass upward throughthe check valve 271 and prevents the lubrication oil from passingdownward through the check valve 271. The check valve 271 may be a ballvalve or a reed valve, or may be a valve other than these. FIGS. 6A and6B show an example in which the check valve 271 is a ball valve. FIG. 6Ashows a state in which the check valve 271 is open and FIG. 6B shows astate in which the check valve 271 is closed.

The check valve 271 includes an inlet 272 through which the lubricatingoil passes to enter an interior of the check valve 27, outlets 274through which the lubricating oil passes to come out of the interior ofthe check valve 27, and an internal flow passage 273 extending from theinlet 272 to the outlets 274. The check valve 271 includes an upstreamstopper 275 provided with the inlet 272 and a valve seat 276, aspherical valve body 277 that closes a space surrounded by the valveseat 276, and a downstream stopper 278 provided with the outlets 274.The check valve 271 may further include a spring that presses the valvebody 277 against the valve seat 276.

The valve body 277 is disposed between the upstream stopper 275 and thedownstream stopper 278. The upstream stopper 275 is disposed under thedownstream stopper 278. Each of the upstream stopper 275 and thedownstream stopper 278 is fixed to an inner wall surface of the bypasspassage 62. The upstream stopper 275 includes a penetrating hole thatpenetrates the upstream stopper 275 in the up/down direction. Similarly,the downstream stopper 278 includes penetrating holes that penetrate thedownstream stopper 278 in the up/down direction. The inlet 272 isprovided at a lower end of the penetrating hole of the upstream stopper275 and the valve seat 276 is provided at an upper end of thepenetrating hole of the upstream stopper 275. The outlet 274 is providedat an upper end of the penetrating hole of the downstream stopper 278.

When the lubricating oil does not flow upward inside the bypass passage62 toward the check valve 271 and an oil pressure applied to the inlet272 of the check valve 271 is low, the valve body 277 is in contact withthe valve seat 276 due to gravity and closes the entire space inside thevalve seat 276. When a flow of the lubricating oil rises inside thebypass passage 62 and the oil pressure applied to the inlet 272 of thecheck valve 271 rises, the valve body 277 moves upward and separatesfrom the valve seat 276. This allows the lubricating oil flowing upwardinside the bypass passage 62 to pass upward through the check valve 271.When the oil pressure applied to the inlet 272 of the check valve 271decreases, the valve body 277 comes into contact with the valve seat 276again.

When the prime mover 3 rotates at low speed, a flow rate of thelubricating oil sent from the gear chamber 30 to the first upstreampassage 56 is low and its pressure is also low. During this time, aportion of the lubricating oil supplied from the first upstream passage56 to the spiral passage 58 does not flow into the internal gap of theupper bearing B1, but flows into the bypass passage 62 or the outerperipheral passage 63 via the merging portion 65. However, during thistime, the check valve 271 is closed and a reverse flow of thelubricating oil at the bypass passage 62 is prevented, so that thelubricating oil flowing from the spiral passage 58 to the mergingportion 65 decreases. The lubricating oil is thus supplied to the upperbearing B1 at a sufficient flow rate, even if the prime mover 3 rotatesat low speed.

Third Preferred Embodiment

A third preferred embodiment of the present invention will be describedbelow. A main difference of the third preferred embodiment with respectto the first preferred embodiment is that a bypass passage 362 of asecond feed passage 352 extends from the first upstream passage 56 tothe return passage 55 not via the first connection passage 53 and thesecond connection passage 54. In the third preferred embodiment, theouter peripheral passage 63 and the merging portion 65 according to thefirst preferred embodiment are not provided.

FIG. 7 is a vertical sectional view showing the interior of the lowercase 17 according to the third preferred embodiment of the presentinvention. In FIG. 7, components equivalent to the components shown inFIG. 1 to FIG. 6B are denoted by the same reference numerals as in FIG.1, etc., and description thereof will be omitted.

The bypass passage 362 extends obliquely upward from the first upstreampassage 56 to the return passage 55. The bypass passage 362 may extendfrom the gear chamber 30 to the return passage 55 not via the firstupstream passage 56. The bypass passage 362 has a cylindrical orsubstantially cylindrical shape inclined obliquely with respect to thecenter line of the driveshaft 5. A center line C1 of the bypass passage362 is a straight line extending from an upstream end of the bypasspassage 362 to a downstream end of the bypass passage 362, for example.An inner diameter of the bypass passage 362 may be constant from theupstream end of the bypass passage 362 to the downstream end of thebypass passage 362, or may decrease step by step or continuously as itapproaches the upstream end of the bypass passage 362.

The upstream end of the bypass passage 362 opens at an inner wallsurface of the first upstream passage 56. The downstream end of thebypass passage 362 is open at the inner surface of the shift chamber 37(an inner wall surface of the return passage 55). FIG. 7 shows anexample in which an upper end 362 a of the downstream end of the bypasspassage 362 is disposed above the upper end of the spiral groove 59 thatcorresponds to the downstream end of the spiral passage 58 and a lowerend 362 b of the downstream end of the bypass passage 362 is disposedbelow the upper end of the spiral groove 59. A distance in the verticaldirection from the upper end 362 a of the downstream end of the bypasspassage 362 to a lower end 54 a of the downstream end of the secondconnection passage 54, that is, a height difference between the upperend 362 a and the lower end 54 a preferably is smaller than the outerdiameter D1 of drive shaft 5 (refer to FIG. 4C). This height differencemay be smaller than the minimum value of the inner diameter of thebypass passage 362.

The bypass passage 362 is a separate passage from the spiral passage 58and does not intersect the spiral passage 58. A flow passage area of thebypass passage 362 is greater than the flow passage area of the spiralpassage 58. In the radial direction of the driveshaft 5, the bypasspassage 362 is located farther outward than the spiral passage 58. Thebypass passage 362 is separated from the spiral passage 58 by thepartition wall 17 z of the lower case 17. The partition wall 17 z ispositioned between the spiral passage 58 and the bypass passage 362 inthe radial direction of the driveshaft 5.

When the prime mover 3 rotates at high speed, a portion of thelubricating oil, which has flowed into the first upstream passage 56from the gear chamber 30 due to rotations of the front gear 22 and therear gear 23, passes through the spiral passage 58, the interior of theupper bear B1, and the downstream passage 61 and then flows into thereturn passage 55. The remaining lubricating oil flows into the returnpassage 55 via the bypass passage 362 without passing through the spiralpassage 58. The lubricating oil is thus circulated at a flow rateexceeding a supply capacity of the spiral passage 58.

Further, although the first feed passage 51 and the second feed passage352 share the first upstream passage 56, the first feed passage 51 andthe second feed passage 352 are separate from each other on a downstreamside of the first upstream passage 56. Thus, the lubricating oil to besupplied from the spiral passage 58 to the interior of the upper bear B1does not flow into the second feed passage 352. The lubricating oil isthus supplied to the interior of the upper bearing B1 at a sufficientflow rate, even if the prime mover 3 rotates at a low speed.

Other Preferred Embodiments

The present invention is not restricted to the contents of the preferredembodiments described above and various modifications are possible.

For example, with the preferred embodiments described above, anon-limiting example in which the first upstream passage 56 ispreferably shared by the first feed passage 51 and the second feedpassage 52 was described. However, the second feed passage 52 mayinclude a second upstream passage separate from the first upstreampassage 56.

With the preferred embodiments described above, a non-limiting examplein which the first upstream passage 56 preferably is adjacent to thelower bearing B2 and the outer peripheral passages 63 preferably areadjacent to the upper bearing B1 was described. However, the firstupstream passage 56 may be separate from the lower bearing B2.Similarly, the outer peripheral passages 63 may be separate from theupper bearing B1.

With the preferred embodiments described above, a non-limiting examplein which the bypass passage 62 preferably is integral with the lowercase 17 was described. However, the bypass passage 62 may be defined bya member separate from the lower case 17.

With the preferred embodiments described above, a non-limiting examplein which the bypass passage 62 preferably is located in front of thedriveshaft 5 was described. However, the bypass passage 62 may belocated to a side or behind the driveshaft 5. The same applies to thefirst upstream passage 56.

For example, as shown in FIG. 8, a bypass passage 462 of a second feedpassage 452 may extend upward, not from the first upstream passage 56,but from the gear chamber 30. FIG. 8 shows an example in which thebypass passage 462 is disposed behind the drive shaft 5. A lower end(upstream end) of the bypass passage 462 opens at an inner surface ofthe gear chamber 30 and an upper end of the bypass passage 462 opens atan upper surface of the lower case 17. The upper end of the bypasspassage 462 is closed by the shaft cap 28. The bypass passage 462 isconnected to the first downstream passage 61 via a second downstreampassage 463.

With the preferred embodiments described above, a non-limiting examplein which both the upper end and the lower end of the bypass passage 62preferably are located at heights between the upper end and the lowerend of the spiral groove 59 was described. However, a portion of thebypass passage 62 may be disposed higher than or lower than the spiralgroove 59.

The cross section of the bypass passage 62 taken along a planeperpendicular or substantially perpendicular to the center line of thedriveshaft 5 (the drive axis Ad) is not limited to have a circular shapeand may have an elliptical or polygonal shape, or may have a C shapeextending along the shaft insertion hole 25. That is, the cross sectionof the bypass passage 62 does not need to have a shape continuous in thecircumferential direction of the drive shaft 5 across an entirecircumference of the drive shaft 5, but may have a shape including twoends spaced apart in the circumferential direction of the drive shaft 5.

As shown in FIG. 4C, the cross section of the bypass passage 62 includestwo ends X1 and X2 spaced apart from each other in the circumferentialdirection of the drive shaft 5. An arc Y1 defines an arc that passesthrough the bypass passage 62 and connects both ends X1 and X2 of thecross section of the bypass passage 62 to each other. An arc Y2 definesan arc that does not pass through the bypass passage 62 and connectsboth ends X1 and X2 of the cross section of the bypass passage 62 toeach other. Each of the arc Y1 and the arc Y2 extends in thecircumferential direction of the drive shaft 5. The arc Y1 may beshorter or longer than the arc Y2 in the circumferential direction ofthe drive shaft 5, or may have a length equal to a length of the arc Y2.

With the preferred embodiments described above, a non-limiting examplein which the lower ends of the outer peripheral passages 63 thatcorrespond to the upstream ends preferably are connected by the mergingportion 65 to the first feed passage 51 was described. However, apartition wall separating the lower ends of the outer peripheralpassages 63 from the first feed passage 51 may be provided in place ofthe merging portion 65.

With the preferred embodiments described above, a non-limiting examplein which the second connection passage 54 preferably is located higherthan the lower end of the upper bearing B1 was described. However, atleast a portion of the second connection passage 54 may be located lowerthan the lower end of the upper bearing B1. In this case, the outerperipheral passages 63 may be omitted. That is, the second connectionpassage 54 may extend from the bypass passage 62 to the return passage55.

Features of two or more of the various preferred embodiments describedabove may be combined.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. An outboard motor comprising: a prime mover; adriveshaft extending in an up/down direction below the prime mover andto which a rotation of the prime mover is transmitted; a gear mechanismcoupled to a lower end of the driveshaft and to which a rotation of thedriveshaft is transmitted; a propeller shaft to which a rotation of thegear mechanism is transmitted; a lower case in which the driveshaft isinserted and defining a gear chamber that houses the gear mechanism anda lubricating oil; an upper bearing located above the gear mechanism androtatably supporting the driveshaft inside the lower case; a feedpassage, through which the lubricating oil flows upward from the gearmechanism due to rotation of the gear mechanism, extending upward fromthe gear chamber; a return passage separate from the feed passage thatreturns the lubricating oil, fed by the feed passage, to the gearchamber; and a connection passage that guides the lubricating oil fromthe feed passage to the return passage; wherein the feed passageincludes: a first feed passage including a first upstream passageextending upward from the gear chamber and a spiral passage spirallysurrounding the driveshaft below the upper bearing, the first feedpassage extending from the gear chamber to the connection passage viathe first upstream passage, the spiral passage, and an interior of theupper bearing, in that order; and a second feed passage including abypass passage that is disposed around the spiral passage, is separatefrom the spiral passage, and includes two ends spaced apart in acircumferential direction of the driveshaft, the second feed passageextending from the gear chamber to the return passage and bypassing thespiral passage due to the bypass passage.
 2. The outboard motoraccording to claim 1, wherein a flow passage area of the bypass passageis greater than a flow passage area of the spiral passage.
 3. Theoutboard motor according to claim 1, wherein the spiral passage includesa spiral groove extending in the up/down direction and spirallysurrounding a center line of the driveshaft; and at least a portion ofthe bypass passage is located at a height between an upper end and alower end of the spiral groove.
 4. The outboard motor according to claim3, wherein both an upper end and a lower end of the bypass passage arelocated at heights between the upper end and the lower end of the spiralgroove.
 5. The outboard motor according to claim 1, wherein the bypasspassage is integral and unitary with the lower case.
 6. The outboardmotor according to claim 1, wherein the connection passage includes anupstream end connected to the feed passage and a downstream endconnected to the return passage; and at least one of the upstream endand the downstream end of the connection passage is located above an oilsurface of the lubricating oil when the prime mover is stopped.
 7. Theoutboard motor according to claim 1, wherein the feed passage includes amerging portion disposed on an upstream side of the connection passageand connecting the first feed passage and the second feed passage toeach other.
 8. The outboard motor according to claim 7, wherein themerging portion connects the first feed passage and the second feedpassage to each other at a location that is upstream of the upperbearing and downstream of the spiral passage.
 9. The outboard motoraccording to claim 7, further comprising a check valve disposed insidethe second feed passage on an upstream side of the merging portion andthat prevents a reverse flow of the lubricating oil in which thelubricating oil inside the second feed passage flows toward the gearchamber.
 10. The outboard motor according to claim 1, wherein the secondfeed passage further includes at least one outer peripheral passage thatbypasses the interior of the upper bearing, and the second feed passageextends from the gear chamber to the return passage via the connectionpassage.
 11. The outboard motor according to claim 10, wherein a portionof the at least one outer peripheral passage is defined by an outerperipheral surface of the upper bearing.
 12. The outboard motoraccording to claim 10, wherein the at least one outer peripheral passageincludes a plurality of outer peripheral passages spaced apart in thecircumferential direction of the driveshaft.
 13. The outboard motoraccording to claim 1, wherein the second feed passage extends from thegear chamber to the return passage via the connection passage; theconnection passage includes a first connection passage and a secondconnection passage that are different from each other; the firstconnection passage guides the lubricating oil from the first feedpassage to the return passage; and the second connection passage guidesthe lubricating oil from the second feed passage to the return passage.14. The outboard motor according to claim 13, wherein the second feedpassage is connected to both the first connection passage and the secondconnection passage.
 15. The outboard motor according to claim 1, whereinthe second feed passage extends from the gear chamber to the returnpassage without passing through the connection passage.
 16. The outboardmotor according to claim 15, wherein the bypass passage extendsobliquely downward from an inner wall surface of the return passage. 17.The outboard motor according to claim 1, wherein the second feed passageextends from the gear chamber to the return passage via the connectionpassage and is separate from the first feed passage at a region from anupstream end of the bypass passage to a location around the upperbearing.
 18. The outboard motor according to claim 17, wherein thesecond feed passage is separate from the first feed passage at a regionfrom the gear chamber to the location around the upper bearing.